Doping effect and oxygen vacancy engineering in nickel-manganese layered double hydroxides for high-performance supercapacitors

Design of electrode materials with high electrochemical capacitance and long lifetime remains a challenging issue for high-performance supercapacitors. Herein, we successfully synthesized a binder-free composite electrode comprising oxygen vacancy-abundant NiMnMg-layered double hydroxides grown on 3D graphene foam (Vo-NiMnMg-LDH@3DG) by Mg doping during hydrothermal process and subsequently Ar plasma etching. Thanks to the incorporation of electrochemically inert Mg element, the enhanced charge transfer capability, and enriched active sites that induced by plentiful oxygen vacancies, Vo-NiMnMg-LDH@3DG manifests a high specific capacity of 374.8 mAh g-1 at a current density of 1 A g-1 and satisfactory rate performance (74.26% at 20 A g- 1). Furthermore, the asymmetric supercapacitor (ASC) assembled with Vo-NiMnMg-LDH@3DG cathode and activated carbon anode exhibits a specific capacitance up to 171 F g-1 at 1 A g-1, achieving a maximum energy density of 53.62 Wh kg-1 and the highest power density of 7500 W kg-1. This work not only provides innovative approaches for preparing oxygen vacancy-rich LDH materials, but also offers insights for the design and improvement of energy storage devices based on transition metal-based LDH.